Emergency crews evacuated homes in Runcorn's Windmill Hill overnight, after a fire and suspected gas leak.
Firefighters were called out just after 2am. Police officers and gas officials then cleared the area.
No-one was injured. People have now been allowed back into the area.
More top news
The threat level has been raised to critical by MI5's Counter-Terrorism Analysis Centre.
Prime Minister Theresa May announced the decision from Downing Street.
In her message Theresa May praised the "inspirational bravery" and "unbreakable spirit" of Mancunians in the wake of the blast.